Need some advice on milk chocolate...
Posted in: Tasting Notes
Crystals won't form at 118. They'll just melt. However you may get some benefit from holding it there for a bit to ensure complete melting of the crystals. - Think ice cube in boiling water. Even though the water is boiling, there can still be ice. But with a little bit of time the ice will melt.
Taking the chocolate to 118 will help ensure you have melted all the pre-existing crystals.
The crystals will form at lower temperatures. The link I posted above really helped me to understand tempering. Take a look. 
